Re: passing-through TOS/DSCP marking

[Florent Daigniere <nextgens@freenetproject.org>]

On Thu, 2021-06-17 at 01:33 +0200, Toke Høiland-Jørgensen wrote:
> Daniel Golle <daniel@makrotopia.org> writes:
> 
> > Hi Jason,
> > 
> > On Wed, Jun 16, 2021 at 06:28:12PM +0200, Jason A. Donenfeld wrote:
> > > WireGuard does not copy the inner DSCP mark to the outside, aside
> > > from
> > > the ECN bits, in order to avoid a data leak.
> > 
> > That's a very valid argument.
> > 
> > However, from my experience now, Wireguard is not suitable for
> > VoIP/RTP
> > data (minimize-delay) being sent through the same tunnel as TCP bulk
> > (maximize-throughput) traffic in bandwidth constraint and/or high-
> > latency
> > environments, as that ruins the VoIP calls to the degree of not
> > being
> > understandable. ECN helps quite a bit when it comes to avoid packet
> > drops
> > for TCP traffic, but that's not enough to avoid high jitter and
> > drops for
> > RTP/UDP traffic at the same time.
> > 
> > I thought about ways to improve that and wonder what you would
> > suggest.
> > My ideas are:
> >  * have different tunnels depending on inner DSCP bits and mark them
> >    accordingly on the outside.
> >    => we already got multiple tunnels and that would double the
> > number.
> > 
> >  * mark outer packets with DSCP bits based on their size.
> >    VoIP RTP/UDP packets are typically "medium sized" while TCP
> > packets
> >    typically max out the MTU.
> >    => we would not leak information, but that assumption may not
> > always
> >       be true
> > 
> >  * patch wireguard kernel code to allow preserving inner DSCP bits.
> >    => even only having 2 differentl classes of traffic (critical vs.
> >       bulk) would already help a lot...
> > 
> > 
> > What do you think? Any other ideas?
> 
> Can you share a few more details about the network setup? I.e., where
> is
> the bottleneck link that requires this special treatment?

I can tell you about mine. WiFi in a congested environment: "voip on
mobile phones". WMM/802.11e uses the diffserv markings; most commercial
APs will do the right thing provided packets are marked appropriately.

At the time I have sent patches (back in 2019) for both the golang and
linux implementation that turned it on by default. I believe that
Russell Strong further improved upon them by adding a knob (20190318 on
this mailing list).

Earlier this month I was approached by a NGO that was trying to do voip
over satlinks in between ships... there too, any solution has to involve
DSCP markings.

Florent